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Commit 6411c1c5 authored by Sharvil Nanavati's avatar Sharvil Nanavati
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Reduce CPU utilization from ~60% to ~10% on busy HCI reads. 

This patch improves RFCOMM throughput and reduces CPU utilization.
Instead of using a counting semaphore to measure bytes and reading
one at a time from the eager reader's buffer, read in bulk based
on the incoming read request size.

Change-Id: I17046bfbc3ca49576a9c82b38911aeb84234881a
parent f6d281ab

system/osi/src/eager_reader.c

+28 −13
Original line number Diff line number Diff line
@@ -86,7 +86,7 @@ eager_reader_t *eager_reader_new( 
  ret->allocator = allocator;

  ret->inbound_fd = fd_to_read;



  ret->bytes_available_fd = eventfd(0, EFD_SEMAPHORE);

  ret->bytes_available_fd = eventfd(0, 0);

  if (ret->bytes_available_fd == INVALID_FD) {

    LOG_ERROR("%s unable to create output reading semaphore.", __func__);

    goto error;
@@ -171,31 +171,46 @@ size_t eager_reader_read(eager_reader_t *reader, uint8_t *buffer, size_t max_siz 
  assert(reader != NULL);

  assert(buffer != NULL);



  size_t bytes_read = 0;



  while (bytes_read < max_size) {

  // If the caller wants nonblocking behavior, poll to see if we have

  // any bytes available before reading.

  if (!block && !has_byte(reader))

      return bytes_read;

    return 0;



    eventfd_t value;

    if (eventfd_read(reader->bytes_available_fd, &value) == -1)

  // Find out how many bytes we have available in our various buffers.

  eventfd_t bytes_available;

  if (eventfd_read(reader->bytes_available_fd, &bytes_available) == -1) {

    LOG_ERROR("%s unable to read semaphore for output data.", __func__);

    return 0;

  }



  if (max_size > bytes_available)

    max_size = bytes_available;



  size_t bytes_consumed = 0;

  while (bytes_consumed < max_size) {

    if (!reader->current_buffer)

      reader->current_buffer = fixed_queue_dequeue(reader->buffers);



    buffer[bytes_read] = reader->current_buffer->data[reader->current_buffer->offset];

    reader->current_buffer->offset++;

    bytes_read++;

    size_t bytes_to_copy = reader->current_buffer->length - reader->current_buffer->offset;

    if (bytes_to_copy > (max_size - bytes_consumed))

      bytes_to_copy = max_size - bytes_consumed;



    memcpy(&buffer[bytes_consumed], &reader->current_buffer->data[reader->current_buffer->offset], bytes_to_copy);

    bytes_consumed += bytes_to_copy;

    reader->current_buffer->offset += bytes_to_copy;



    // Prep for next byte

    if (reader->current_buffer->offset >= reader->current_buffer->length) {

      reader->allocator->free(reader->current_buffer);

      reader->current_buffer = NULL;

    }

  }



  return bytes_read;

  bytes_available -= bytes_consumed;

  if (eventfd_write(reader->bytes_available_fd, bytes_available) == -1) {

    LOG_ERROR("%s unable to write back bytes available for output data.", __func__);

  }



  return bytes_consumed;

}



static bool has_byte(const eager_reader_t *reader) {